1. Field of Invention
The present invention relates to a brushless direct current (DC) motor and driving unit thereof, and in particular to a brushless DC motor and driving unit thereof including a stator which has a plurality of alternately arranged upper pole arms and lower pole arms.
2. Related Art
Please refer to FIG. 1, which shows a conventional driving circuit of a motor. A driver 10 is electrically connected with a main power Vcc. A bridge circuit 12 includes four switches Q1˜Q4 and a coil L, and the bridge circuit 12 is electrically connected with the driver 10 and a main power source Vcc. The driver 10 receives the required voltage from the main power source Vcc and outputs the controlling signal C1 and the controlling signal C2 to the bridge circuit 12 for switching on and switching off the witches Q1˜Q4.
The conventional motor is mainly composed of a rotor, a magnet ring disposed in the rotor, a stator and a printed circuit board. The stator includes a plurality of salient poles located at the same level, and the driver 10 and a sensor 14 are disposed on the printed circuit board.
The coil L of the bridge circuit 12 is wound on the stator. When the motor operates, the driver 10 outputs the controlling signal C1 and the controlling signal C2 to the bridge circuit 12 for switching on and switching off the witches Q1˜Q4. While the switch Q1 and the switch Q4 of the bridge circuit 12 are turned on and the switch Q2 and the switch Q3 of the bridge circuit 12 are turned off, the electric current flows through the switch Q1, the coil L and the switch Q4. On the other hand, while the switch Q2 and the switch Q3 of the bridge circuit 12 are turned on and the switch Q1 and the switch Q4 of the bridge circuit 12 are turned off, the electric current flows through the switch Q2, the coil L and the switch Q3. The rotor is driven by the electromagnetic field on the stator when the electric current flows through the coil L. The sensor 14 senses the magnetic field of the magnet ring of the rotor and outputs a sensing signal Ssense to the driver 10 for adjusting the time that the electric current flowing through the coil L, so as to make a stable electromagnetic field on the stator.
However, the conventional motor has greater Cogging Torque, and there is a short “dead time” during the switch of the flowing direction of the electric current, so that the amplitude of vibration between the highest current and the lowest current is too wide, and the electronic elements in the motor are broken by an excessive Peak Current easily. If the conventional motor is applied to a fan, the multiple-frequency vibration of the motor will be apparent on the fan. In addition, there are only one driving circuit, one single coil L and one set of salient poles in the stator of the conventional motor, if anyone of the electronic elements mentioned above is broken, there will be no electromagnetic field on the stator and the rotor will stop rotating.